The Blended Care Intervention "Booster" for Youth With Chronic Health Conditions to Increase Fatigue-related Self-efficacy

Single-item question, self-report via Booster app. The single item was designed and validated for this study. Answered on a VAS scale 0 to 100. Higher score represents higher fatigue-related self-efficacy.

pediatric short fatigue questionnaire, 4-item questionnaire, answered on a seven point Likert scale (1 = yes that is true, 7=no, that is not true). Total score ranges from 4 to 28, with higher scores reflecting more fatigue.

School or work presence. Calculated: (hours present/the hours scheduled)*100

Cantril Ladder, single-item question, rate life with ladder numbered from 0 to 10. Top of the ladder (10) represents the best possible life. The bottom (0) represents the worst possible life.

EuroQol (EQ) visual analogue scale (VAS), ranging from 0 (worst health you can imagine) to 100 (best health you can imagine).

Self-Efficacy Scale-28 (SES-28) , 7-item questionnaire answered on a four-point likert scale, total scores range from 7 to 28 with higher scores indicating higher sense of control over fatigue.

PEDsQL-MFS, 23-item questionnaire

Pediatric Quality of Life Inventory-Multidimensional Fatigue Scale (PEDsQL-MFS), 24-item questionnaire answered on a five-point likert (0=never, 4 = almost always), total score ranging from 0 to 96, with higher scores representing more fatigue.

Pediatric Quality of Life Inventory-Generic Core Scales (PEDsQL-GCS), a 23-item questionnaire answered on a five-point likert (0=never, 4 = almost always), total score ranging from 0 to 92, with higher scores representing higher quality of life. The questionnaire has the following subscales: physical, emotional, social and school or work functioning.

Child Health Utility Index 9D (Chu9d), nine-item questionnaire answered on a five-point likert (0 to 4), total score ranging from 0 to 36, higher scores representing lower quality of life. The Chu9D has utility values that enable calculating quality adjusted life years.

EuroQol Five Dimensions Health Questionnaire Youth (EQ-5D-Y-3L), five-item questionnaire answered on a three point likert (no problems (1), some problems(2), a lot of problems(3)), total score ranging from 5 to 15, higher scores representing lower quality of life. The EQ-5D-Y-3L has utility values that enable calculating quality adjusted life years.

Single item question on average absence over past half a year in %

Illness identity questionnaire (ILQ), a 25-item questionnaire, answered on a five-point Likert scale ranging from 1 (strongly disagree) to 5 (strongly agree). It has the following subscales: engulfment (8 items, range 8 to 40), rejection (5 items, range 5 to 25), acceptance (5 items, range 5 to 25) and enrichment (7 items, range 7 to 35). Higher scores on subscales represent respectively higher engulfment, rejection, acceptance and enrichment. The questionnaire is adapted to specifically ask for illness identity regarding fatigue (e.g., I refuse to see my fatigue as part of myself)

Pearlin Schooler Mastery Scale, a seven-item questionnaire, answered on a four-point Likert scale, ranging from strongly disagree (1) to strongly agree (4). Total score ranges from 7 to 28, with higher scores reflecting higher levels of mastery.

Physical Activity Questionnaire for Adolescents (PAQ-A), a nine-item questionnaire. The first eight items are answered on a five-point Likert scale, ranging from low (1) to high (5) levels of physical activity. The ninth item asks whether the past week's activity was typical, less than typical, or more than typical, to provide context for the responses.The total score is calculated by averaging the scores of the first 8 items, yielding a final score ranging from 1 to 5. Higher scores indicate higher levels of physical activity.